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A small hybrid rocket engine has been developed, which has radial and swirl two hollow injectors, a large quarts glass window, a transparent combustion chamber and a divergent nozzle. Flame behaviors under atmospheric pressure combustion have been taken by high-speed photography with 30,000 FPS. The proper orthogonal decomposition (POD) is applied to the luminous intensity of acquired images. The higher POD modes are found to capture the structures of luminous flame streaks and the peak frequency of mode 2 coefficient is found to have some relation with the oscillation frequency of the boundary layer.
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Experimental methods for determining dynamic characteristics of landing gears are considered. The main dynamic characteristics of landing gears are resonant frequencies, damping coefficients and resonant oscillation shapes. * Features of ground vibration testing for landing gears * Methods for determining main normal modes * Processing algorithms * Application of impact method * Influence of hydraulic rams on landing gear dynamic characteristic
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  • Document
The results of experiments on transonic buffet control by means of \"plasma wedge\" actuators basing on spark discharge are discussed. Experiments have been carried out in the range of Mach number 0.730.78 using model of rectangular wing with supercritical airfoil, chord 200 mm and span 599 mm. Schlieren visualization and Pitot measurements in the wake of the wing show that actuators effectively influence on mean flow and characteristics of shock wave oscillations. It was also found that control efficiency depends on frequency of discharge.
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  • Document
The flow pattern in over-expanded conical nozzles is numerically investigated by means of threedimensional wall-modeled large-eddy simulations (WM-LES). The objective of the study is to identify the origin of the low-frequency oscillations (LFO) and the side-loads generation observed in separated supersonic flows. The computational results are compared with the available experimental data for validation. The simulations bring clear evidence of the existence of broadband and energetically-significant LFO in the vicinity of the separated shock. The magnitude of the shock excursions was less important in the conical case, compared to the planar nozzle, because of the strong adverse pressure gradient that develops upstream of the separation zone. The generated side-loads were analyzed and a dynamic mode decomposition (DMD) analysis reveals the existence of two types of modes: the non-helical modes which are low-frequency modes based mainly in the streamwise forces and the helical modes which are highfrequencies modes, compared to the first Type. The laters mainly concern the side-loads.
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  • Document
The flame stabilization represents a relevant issue in aero-engine design. In fact, the growing demand of pollutant emissions reduction without significant losses of the combustion efficiency has driven the efforts of the scientific community towards lean flames. Lean fuel mixtures, characterized by low temperature flames, could manifest an unstable behaviour which can easily lead to the flame extinction due to the establishment of the blowout condition. This requires the implementation of control systems to avoid flame instability occurrence. The present work shows an investigation of the impact of dielectric barrier discharge (DBD) plasma actuation on lifted flame stabilization in a methane CH4-air Bunsen burner at ambient conditions. Two different plasma actuator configurations, powered with a high voltage (HV)/high frequency sinusoidal signal, have been investigated. Once the best actuator configuration was selected, the efficiency of the plasma actuation has been evaluated in terms of the flame lift-off distance, length and shape. In particular, in order to change the actuator power dissipation, different peak-to-peak voltages Vpp were tested, while the actuation frequency was kept equal to 20 kHz. The application of plasma discharges to flame stabilization leads to plasma-attached flames or plasma-enhanced lifted flames, depending on the air and fuel flow rates. At air flow rate of 1.54 g/s, plasma actuation allowed to decrease the lift-off height until the fuel jet velocity was below about 0.05 m/s thanks to the extension of the flame region upstream, toward the burner exit section. Beyond this value, it had no significant impact on the flame lift-off height, even though the amplitude of the lift-off height oscillations reduced coupled with a more stable behaviour of the lifting flame. The benefit of the plasma actuation increased by reducing the air flow rate to 1.35 g/s. In this condition, plasma-assisted flame reattachment was evident at each fuel velocity, in combination with an increasing flame height proportionally to the fuel jet velocity.
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  • Document